The present invention relates to magnetic materials, and more particularly relates to magnetic nanocomposite materials including samarium, cobalt, iron, copper, zirconium and carbon which have favorable magnetic properties and are suitable for making bonded magnets.
The Sm(Co,Fe,Cu,Zr)z sintered magnets exhibit outstanding thermal stability and high energy products at elevated temperatures due to their high Curie temperature and spontaneous magnetization. See K. J. Strnat, Proceeding of IEEE, Vol. 78 No. 6 (1990) pp. 923; and A. E. Ray and S. Liu, Journal of Materials Engineering and Performance, Vol. 2 (1992) pp. 183. However, sintered magnets are very hard and brittle, which makes final finishing very costly and may reduce the production yield rate significantly. The near net-shape production enables Sm(Co,Fe,Cu,Zr)z bonded magnets to be used for many sophisticated applications. In our previous work, we focused on the magnetic properties and developed Sm(Co,Fe,Cu,Zr)z powders for bonded magnet applications using conventionally cast alloys. See W. Gong, B. M. Ma and C. O. Bounds, J. Appl. Phys. Vol. 81 (1997) pp. 5640; W. Gong, B. M. Ma and C. O. Bounds, J. Appl. Phys. Vol. 83 (1998) pp. 6709; and W. Gong, B. M. Ma and C. O. Bounds, J. Appl. Phys. Vol. 83 (1998) pp. 6712. Our studies ranged from the effects of phase transformation, solid solution and aging heat-treatments, the particle size and distribution, and the consolidating pressure on the magnetic properties of bonded magnets.
Carbon is a common impurity found in the conventional cast Sm(Co,Fe,Cu,Zr)z alloys. It forms carbides and exhibits a negative impact on the intrinsic coercivity, Hci, and maximum energy product, (BH)max. Recently, C additions have been found to change the lattice parameters and, consequently, the magnetic anisotropy of many Sm2Fe17-based compounds prepared by casting. See B. G. Shen, L. S. Kong, F. W. Fang and L. Cao, J. Appl. Phys. Vol. 75 (1994) pp. 6253. Moreover, the melt spinning technique has been applied to this alloy system and has shown many interesting results. See Z. Chen and G. C. Hadjipanayis, J. Magn. Magn. Mate. Vol. 171 (1997) pp. 261. It is of interest to incorporate carbon into the conventional Sm(Co,Fe,Cu,Zr)z alloys system and to compare its impact on the structural and magnetic properties of materials prepared by different synthesizing methods.
It is the object of the present invention to provide compositions nanocomposite in nature.
It is the further object of the present invention to obtain isotropic magnetic properties.
It is an object of the present invention to obtain compositions comprising, preferably predominately, the SmCoC2 phase.
Another object of the present invention is to provide compositions which require short thermal processing time and or low processing temperature to fully develop favorable magnetic properties.
These and other objects of the present invention will become more apparent from the following description and examples.
The magnetic nanocomposite compositions of the present invention include samarium (Sm) and cobalt (Co), copper (Cu) and iron (Fe), zirconium (Zr) and carbon (C). Preferably, compositions having a predominately SmCoC2 phase. These compositions provide powder-bonded type magnets with favorable magnetic properties. The compositions are preferably rapidly solidified by conventional methods, most preferably by melt spinning, followed by thermally treating the material to form crystalline magnetic phases.